Thermal sleeve

ABSTRACT

A replacement thermal sleeve with a flange for a reactor vessel closure head penetration adapter housing. By altering a diameter of the flange, a replacement thermal sleeve can be installed through the narrow diameter of the penetration adapter housing opening from under the reactor vessel head. The flange can be compressible or expandable or the tubular wall of the thermal sleeve can be inserted in longitudinal sections, one at a time, into an opening in the underside of the penetration head adapter and reformed within the opening when fully inserted.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims the priority benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 62/629,339 filed on Feb. 12,2018, the contents of which are herein incorporated by reference.

FIELD OF THE INVENTION

This invention pertains generally to thermal sleeves and, moreparticularly, to thermal sleeves that can be relatively easily installedand replaced. This invention also pertains to methods of installing andreplacing thermal sleeves.

BACKGROUND OF THE INVENTION

In response to operational experience at a number of nuclear plantsthere is a clear need for a quickly deployed thermal sleeve replacementfor the thermal sleeves in the reactor vessel closure head penetrationadapter housing. Thermal sleeve flange wear is a phenomenon firstidentified domestically in 2014 when a part-length sleeve failed. Sincethen inspections have been recommended and acceptance criteria have beendeveloped. More recently (December 2017), two additional thermal sleevefailures at rodded locations were identified.

A sectional view of an example arrangement of a conventional thermalsleeve 10 positioned in a guide funnel 12 of a reactor head penetrationadaptor 14 within a control rod drive mechanism (CRDM) 16. When athermal sleeve 10 fails at an upper flange 18 location at a roddedlocation, the only current repair is the complex removal of the CRDM 16and reinstallation of a new sleeve 10 and guide funnel 12. Thisreplacement can take several weeks and is required, because the upperflange 18 is integral to the thermal sleeve 10 and fully captured in thehead penetration adapter 14.

Accordingly, it is an object of this invention to provide a new thermalsleeve design and method of installation that will reduce the timerequired for thermal sleeve replacement and avoid the requirement toremove the CRDM.

SUMMARY

This invention achieves the foregoing objective in one embodiment byproviding a replacement thermal sleeve comprising an elongated tubularsheath having a wall with a radially, outwardly extending flange at oneend of the wall and an axis extending along the elongated dimension. Aplurality of slots extend axially in the wall of the elongated tubularsheath with the slots extending through the flange and along the sheatha preselected distance that does not extend to another end of the wallof the sheath. In one such embodiment the slots have a width sufficientto facilitate compression of the flange to narrow an outside diameter ofthe flange in the compressed state to an extent necessary to clear anyobstruction in an opening of a tubular member in which the thermalsleeve is to be inserted. The slots define a flexible leaf between eachtwo adjacent slots. In one embodiment the plurality of slots are twoslots formed 180 degrees apart around the circumference of the wall. Inone such alternate embodiment the plurality of slots are three slotsformed 120 degrees apart around the circumference of the wall. In stillanother such embodiment, the plurality of slots are four slots formed 90degrees apart around the circumference of the wall.

In another embodiment, in a relaxed state, at the flange, the leafssubstantially touch each adjacent leaf and the leafs are configured sothat if spread apart at the flange to a point where the width of theslot is sufficient to seat the flange in a recess in the opening of thetubular member in which the flange is to be seated to lock thereplacement thermal sleeve in the opening, then the leafs experienceplastic deformation.

The invention also includes a method of replacing a damaged thermalsleeve in a reactor vessel head adapter that connects a control roddrive mechanism to a reactor vessel head. The method includes the stepof accessing the damaged thermal sleeve from an underside of the reactorvessel head. The method then removes the damaged thermal sleeve and, inone embodiment, obtains a replacement thermal sleeve. The replacementthermal sleeve has an elongated tubular sheath having a radially,outwardly extending flange at one end; an axis extending along theelongated dimension; and a plurality of axially extending slots in andthrough the wall of the elongated tubular sheath. The slots extendthrough the flange and along the sheath a preselected distance that doesnot extend to another end of the wall of the sheath and have a widthsufficient to narrow an outside diameter of the flange to at least anextent necessary to clear any obstruction in an opening of the reactorhead adapter in which the thermal sleeve is to be inserted, whenadjacent sections of the flange in between the slots substantiallytouch. The slots define a leaf in between each two adjacent slots. Themethod then alters the diameter of the flange on the replacement thermalsleeve to an extent necessary to clear any obstruction in the opening inthe tubular member that will be encountered while inserting thereplacement thermal sleeve to a location within the opening originallyoccupied by the damaged thermal sleeve; and inserts the replacementthermal sleeve through the opening from the underside of the reactorvessel head. Finally the method expands the diameter of the flange intoa recess in the opening in the reactor head adapter.

In one embodiment, the activation of the steps of altering the diameterof the flange, comprises exerting a compressive force to compressadjacent sections of the flange together, and expanding the diameter ofthe flange, comprises removing the compressive force, and both steps areperformed from the underside of the reactor vessel head. In such anembodiment the steps of compressing the flange and releasing thecompressed flange is preferably performed by either a tool inserted fromthe underside of the reactor vessel head that grips recesses in an uppersurface of the flange or a retention strap installed below the flange.

In still an alternate embodiment of the method the step of altering thediameter of the flange is performed during manufacture of thereplacement thermal sleeve and the step of expanding the diameter of theflange is performed from the underside of the reactor vessel headadapter.

The invention also contemplates a replacement thermal sleeve having aplurality of longitudinal wall sections, with each wall section having aradially outwardly extending flange segment at one end, that when thelongitudinal wall sections are fitted together, configure a tubular wallof the replacement thermal sleeve. This latter embodiment of thereplacement thermal sleeve also includes a fastener for fastening theplurality of longitudinal wall sections together. One such embodimentfor replacing a thermal sleeve in a reactor closure head penetrationadapter may configure the longitudinal wall sections to be inserted oneat a time into an opening in an underside of the reactor head adapterand the fastener is configured to be applied from an underside of thereactor closure head penetration adapter. The plurality of longitudinalwall sections may also comprise three wall sections.

The invention further contemplates a method for installing the latterembodiment of the replacement thermal sleeve. The method comprisesaccessing the damaged thermal sleeve from and underside of the reactorvessel head adapter. The damaged thermal sleeve is removed and areplacement thermal sleeve is obtained, with the replacement thermalsleeve divided into a plurality of longitudinal wall sections. Theplurality of longitudinal wall sections are inserted into an opening inthe underside of the reactor vessel head adapter, one at a time. Thenthe longitudinal wall sections are arranged within the opening into atubular housing of the replacement thermal sleeve. The longitudinal wallsections are then fastened together from the underside of the reactorvessel head adapter.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the invention can be gained from thefollowing description of the preferred embodiments when read inconjunction with the accompanying drawings in which:

FIG. 1 is a schematic cross-sectional view of a conventional reactorvessel head penetration showing a head adapter, thermal sleeve andControl Rod Drive Mechanism (CRDM) latch housing;

FIGS. 2A and 2B are perspective views of a compressible thermal sleevein accordance with one example embodiment of the present inventionshown, respectively, with a flanged end in a relaxed state and in aradially compressed state;

FIGS. 3A and 3B are schematic views of the thermal sleeve of FIGS. 2A-2Bshown, respectively, in a first, radially compressed, positioning beinginserted through a reactor head adaptor (shown sectionally) and in asecond, relaxed, positioning installed in the reactor head adaptor;

FIGS. 4A-4E are schematic views of the thermal sleeve of FIGS. 2A-2B(shown sectionally in FIGS. 4C-4E) in various stages of compression andexpansion as the thermal sleeve is manipulated by an example compressiontool during installation of the thermal sleeve in a reactor head adaptor(shown sectionally);

FIGS. 5 and 6 are perspective views of different variations of thermalsleeves in accordance with example embodiments of the present invention;

FIG. 7 is a perspective view of another embodiment of a compressiblethermal sleeve in accordance with an example embodiment of the presentinvention with fingers in between the leafs having flange lugs;

FIG. 8A is an axial view of the thermal sleeve of FIG. 7 in a relaxedconfiguration;

FIG. 8B is a plan view of the thermal sleeve of FIG. 7 with the flangelugs and inserts in a radially compressed, collapsed configuration;

FIG. 8C is a perspective view of the thermal sleeve of FIG. 8B;

FIGS. 9A and 9B are perspective views of yet another thermal sleeve inaccordance with another example embodiment of the present inventionshown, respectively, with a flanged end in a first relaxed state and insecond relaxed state after plastic deformation of a portion of thethermal sleeve has occurred;

FIGS. 10A-10C are schematic views showing the thermal sleeve of FIGS.9A-9C in different stages of installation within a reactor head adaptor(shown sectionally);

FIGS. 11A-11E are schematic views showing the thermal sleeve of FIGS. 9Aand 9B along with example installation tooling in different stages ofinstallation within a reactor head adaptor (shown sectionally);

FIG. 12 is a perspective view of another example thermal sleeve inaccordance with another example embodiment of the present invention inwhich the sleeve is formed from a plurality of leafs;

FIG. 13 is a perspective view of one of the sectioned leafs of thethermal sleeve of FIG. 12;

FIGS. 14A-F are axial views illustrating the steps in assembling thesegmented leafs of the thermal sleeve of FIG. 12 in an adapter opening;

FIG. 15 is a perspective view further illustrating the arrangement ofleafs of FIGS. 14E and 14F in the adapter opening;

FIGS. 16A-C, respectively, show views of the segmented thermal sleeve ofFIG. 12 in example assembled configurations;

FIGS. 17A and 17B, respectively, are perspective views of the collar andnut employed to lock the leafs of the thermal sleeve arrangement of FIG.12 in place within an adapter opening;

FIG. 18 is a perspective view of the segmented leaf tabs in place on thecollar of FIG. 17A;

FIG. 19 is a sectional elevation view showing the nut of FIG. 17B fullyassembled over the collar and leaf arrangement of FIG. 17A; and

FIG. 20 is a perspective view illustrating the area over which the nutof FIG. 17B is crimped onto the collar of FIG. 17A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

One object of the present invention is to avoid the requirement toremove the CRDM in order to access and remove the thermal sleeve toshorten the time it takes to replace a thermal sleeve in a reactor headadapter. Reducing the time required for a thermal sleeve replacement andproviding options on how to do so will be tremendously valuable to theindustry as thermal sleeve failures become more prevalent and regularinspections are performed to identify such failures. This invention is are-design of the thermal sleeve that can be installed without the CRDMremoval process. To achieve this, embodiments of the present inventionprovide for the flange on the lead end of the thermal sleeve to bedeformed or disassembled in various ways such that the flange can passthrough the narrowest inner diameter of the opening in the reactor headadaptor through which the flange is to be inserted.

Referring now to FIGS. 2A and 2B, a thermal sleeve 20 in accordance withan example embodiment of the present invention is shown. Thermal sleeve20 is formed generally as an elongated tubular body 22 disposed about acentral longitudinal axis 24 and extending between a bottom end 26 and atop end 28. Thermal sleeve 20 includes a flanged region 30 disposed ator about top end 28 which extends radially outward from tubular body 22(i.e., away from axis 24). As shown shifting from FIG. 2A to FIG. 2B,flanged region 30 may be deformed inward (i.e., toward axis 24) when apredetermined force F is applied to flanged region 30. To provide forsuch deformation of flanged region 30, thermal sleeve 20 includes aplurality (three are shown in the illustrated example) of slots 32defined in tubular body 22, with each slot 32 extending through and fromtop end 28 toward bottom end 26. As a result of such slots 32, flangedregion 30 is thus divided in a plurality of segmented flange lugs 33,with each flange lug 33 being spaced from each adjacent flange lug by arespective slot 32 of the plurality of slots 32. Each slot 32 extends apredetermined distance L along tubular body 22 without extending throughbottom end 26 thereof. Additionally, each slot 32 has a maximum width W(generally circumferential to axis 24) which is sufficient to narrow amaximum outside diameter of flanged region 30 from a first diameter D1(FIG. 2A) to a second diameter D2 (FIG. 2B) in order to clear anyobstruction in an opening of a tubular member in which thermal sleeve 20is to be inserted.

As shown in FIGS. 3A and 3B, such slotted design allows for elasticcompression of the slotted portion of tubular body 22, and thus flangedregion 30 thereof, such that the resulting outer diameter D2 of flangedregion 30 is less than the narrowest inner diameter ID of opening 34 inhead penetration adapter 14 (shown in section in FIGS. 3A and 3B, seealso FIG. 1) through which thermal sleeve 20 it is to be inserted.

As shown in FIGS. 4A-4E, temporary compression of flanged region 30 ofthermal sleeve 20 may be achieved with specialized tooling 40 thatinterfaces with a top flange face 42 of thermal sleeve 20, e.g., viaretractable arms 43 of tooling 40 selectively engaging recesses 44 (FIG.2A) formed therein or a retention strap stored below the flange (notshown in the figures). Once compressed, replacement sleeve 20 isinserted through the bottom of the head penetration adaptor 14, such asshown in FIG. 4A. Once sleeve 20 is positioned at an installationelevation, tooling 40 releases the compression in a controlled mannerand disengages flanged region 30, such as shown in FIGS. 4C and 4D. Thetooling 40 is then removed downward through the shaft of headpenetration adaptor 14, such as shown in FIG. 4E.

Referring to FIG. 5, thermal sleeve 20 may be provided as a full-lengththermal sleeve. Such embodiment is for use after the entirety of theoriginal thermal sleeve has been completely removed and is installed inthe head penetration adaptor 14 in the same manner such as previouslydiscussed. In such embodiment, the bottom end 26 of tubular body 22 mayinclude a funnel 50 to allow guidance of the drive rod into thermalsleeve 20. Funnel 50 may be integral to tubular body 22 or attachedseparately via any suitable process or arrangement.

Referring to FIG. 6, thermal sleeve 20 may be of a sufficiently shortlength so as to be fully contained within the head penetration housing14. In such example, tubular body 22 may include a boss 52 positioned atthe bottom end 26 thereof having a greater outer diameter than tubularbody 22 in order to assist in centering the thermal sleeve 20 within thehead penetration housing 14. The inner diameter of the bottom end 26 oftubular body 22 includes a lead-in chamfer to aid in drive rod insertionthereto. This design can be used with an extension tube attacheddirectly to the bottom of the head penetration housing 14. Thisembodiment may be used with a guide sleeve adaptor 54 also formed from atubular body 56. Guide sleeve adaptor 54 includes a plurality ofalignment tabs 58 that each extend from a top end 60 thereof and thatare positioned so as to align top end 60 of guide sleeve adaptor 54 withbottom end 26 of tubular body 22 of short thermal sleeve 20. Once inplace, guide sleeve adaptor 54 solidly attaches to short thermal sleeve20 and thus generally functions as a guide sleeve.

Referring now to FIGS. 7 and 8A-8C, a compressible thermal sleeve 120 inaccordance with another example embodiment of the present invention isshown. Thermal sleeve 120 is of generally similar design as thermalsleeve 20 (previously discussed) except thermal sleeve 120 furtherincludes a plurality of inserts 160 which extend generally from bottomend 126 to flanged region 130 at or about top end 128 of tubular body122 in each of slots 132, such that each slot 132 is generally dividedinto two by each insert 160. Accordingly, in such arrangement, eachinsert 160 is disposed circumferentially between a pair of segmentedflange lugs 133 in a manner that prevents adjacent flange lugs 133 frommoving inward towards axis 124. Radial compression of sleeve 120 afterinstallation is a concern because downward loads on sleeve 120 couldcause flanged region 130 thereof to compress radially inward and slidedown the penetration and/or contact the control drive rod. Unlike eachof flange lugs 133 which are particularly arranged so as to interactwith a head penetration adaptor 14 (similar to flange lugs 33 previouslydiscussed), each insert 160 does not extend outward and thus does notinterface with head penetration adaptor 14 (and thus are not forcedinward when sleeve 120 is pulled downward). Because inserts 160 are notforced to move radially, they will remain circumferentially between, andthus be “pinched” by the flange lugs 133 as flange lugs 133 are pushedradially inward. The interference between flange lugs 133 and inserts160 prevents lugs 133 from moving inward enough to contact the drive rodor fit into the narrower portion of head penetration adaptor 14. Asshown in FIG. 8B, the plurality of inserts 160 are designed to be ableto fit within the space (not numbered) of the flange lugs 133 when thesleeve 120 is in the collapsed configuration. Pre-installationmanipulation is required to place sleeve 120 in this configuration, soit cannot be achieved during operation. To achieve this configurationfor installation into the penetration adapter opening, inserts 160 arefirst compressed by first forces F1 (FIG. 8A) into the center of theflange opening, as shown in the end view of FIG. 8B and the perspectiveview of FIG. 8C. Next the flange lugs 133 are compressed by a secondforce F2 (FIGS. 8A and 8C) until they are substantially touching asshown in the end view of FIG. 8B and the perspective view of FIG. 8C.Inserts 160 spring back into their required position between each offlange lugs 133 in the same manner as the flange lugs 133 when thethermal sleeve 120 is fully inserted in the head penetration adapter 14.

Referring now to FIGS. 9A, 9B, 10A-10C, and 11A-11E, a compressiblethermal sleeve 220 in accordance with another example embodiment of thepresent invention is shown. Thermal sleeve 220 is of generally similardesign as thermal sleeve 20 (previously discussed) except thermal sleeve220 further includes/utilizes a flanged region 230 which is expandable.By manufacturing thermal sleeve 220 with a flanged region 230 having aninitially reduced outer diameter D2, a replacement sleeve 220 may beinstalled through the narrowest inner diameter ID of the opening 34 inhead penetration adapter 14 (shown in section in FIG. 3, see alsoFIG. 1) through which thermal sleeve 220 it is to be inserted.Installation of thermal sleeve 220 relies on plastically deformingflange segments 233 radially outward. This process is figurativelyillustrated in FIGS. 10A-10C and 11A-11E. Such plastic deformation isachieved through a tool 240 (FIGS. 11A-11E), such as a mandrel.Installation tooling 240 is initially inserted through sleeve 220 so asto be disposed above top end 228 to engage at the top of flanged region230. Once thermal sleeve 220 has been inserted into head penetrationadaptor 14 (with tooling 240 at the leading end of thermal sleeve 220),such as generally shown in FIG. 11B, tooling 240 is disengaged fromthermal sleeve 220 and is pulled down through thermal sleeve 220 forremoval, such as generally shown in FIGS. 11C-11E. During such removal,each of flanged segments are expanded (or swaged) such that they areplastically deformed to the larger outer diameter D1 which is greaterthan the inner diameter ID of head penetration adaptor 14.

Referring now to FIGS. 12-20, a thermal sleeve 320 in accordance withyet another example embodiment of the present invention is shown.Thermal sleeve 320 includes a tubular body 322 comprised of at leastthree separate leafs 322A, 322B, 322C which each extend axially (i.e.,parallel to axis 324) from bottom end 380 to top end 328 of sleeve 320.More particularly, thermal sleeve 320 is sectioned into three leafs thatrespectively have a maximum width W_(MAX) (FIG. 13) that is less thannarrowest inner diameter ID of head penetration adapter 14. As discussedbelow, leafs 322A, 322B and 322C are secured to a spacing collar 382 viaa nut 384.

Referring to FIG. 13, each leaf 322A, 322B, 322C is of similarconstruction and includes a flange lug 333 disposed at or about top end328 and a tab 370 disposed at an opposite end 380. During assembly, eachleaf 322A, 322B, 322C is first inserted through nut 384 which is slidpart-way up leafs 322A, 322B, 322C so as to generally be out of the way.Next, each leaf 322A, 322B and 322C is inserted into head penetrationadaptor 14 individually, and then arranged in a circular patternunderneath the reactor vessel head as described in detail in FIGS.14A-14F, as well as FIG. 15, which illustrates how the at least one ofleafs (e.g., 322C), must be generally elevated (i.e., protruded furtherinto adaptor 14) such that the flange lug 333 thereof will clear theother two leafs (e.g., 322A and 322B) as they are moved into thefinished circular/tubular arrangement such as shown in FIG. 16. Afterleafs 322A, 322B and 322C are arranged in the final arrangement shown inFIG. 16, spacing collar 382 (e.g., FIG. 17) is positioned generallyradially within, and circumferentially between, tabs 370 of leafs 322A,322B, 322C, such as shown in FIG. 18. The arrangement of tabs 370 andspacing collar 382 is then secured with a nut 384 which is slid downalong the arrangement of leafs 322A, 322B, 322C and down around tabs 370thereof and spacing collar 382 which generally forces each tab 370toward spacing collar 382. Nut 384 is then threadingly engaged withspacing collar 382 and then crimped into place on spacing collar 382,such as shown generally at 386 in FIG. 20, to prevent disassembly of thecombination of leafs 322A, 322B, 322C, spacing collar 382 and nut 384.

The current thermal sleeve replacement procedure can take as much as 6-8weeks, in an emergency situation. Since such a repair would not be aplanned outage activity, it would likely extend the plant outagecritical path. Such an extension of a plant outage could cost millionsof dollars in downtime. The anticipated time for the removal of theexisting sleeve (or remnants) and installation of this replacement is onthe order of a few days or less. The components of this invention aresimple and relatively inexpensive to manufacture. They are very similarto the original thermal sleeve design, so the experience to manufacturethem already exists.

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. Accordingly, theparticular embodiments disclosed are meant to be illustrative only andnot limiting as to the scope of the invention which is to be given thefull breadth of the appended claims and any and all equivalents thereof

What is claimed is:
 1. A replacement thermal sleeve comprising: anelongated tubular body disposed about a central longitudinal axis andextending between a bottom end and a top end; a flanged region disposedat or about the top end which extends radially outward from the tubularbody; and a plurality of slots defined in the tubular body, each slotextending through and from the top end toward the bottom end along apredetermined distance, each slot having a width which is sufficient tonarrow a maximum outside diameter of the flanged region from a firstdiameter to a second diameter in order to clear any obstruction in anopening of a tubular member in which the thermal sleeve is to beinserted.
 2. The replacement thermal sleeve of claim 1, wherein theplurality of slots comprise three slots spaced 120 degrees around acircumference of the elongated tubular body.
 3. The replacement thermalsleeve of claim 1, wherein the plurality of slots comprise four slotsspaced 90 degrees around a circumference of the elongated tubular body.4. The replacement thermal sleeve of claim 1, wherein the flanged regionincludes recesses or openings in an end surface thereof which arepositioned and structured to be engaged by tooling for altering themaximum outside diameter of the flanged region.
 5. The replacementthermal sleeve of claim 1, wherein adjacent slots of the plurality ofslots each define a leaf portion of the tubular body which extends fromthe bottom end to the top end; and wherein the leafs are configured tobe elastic so that when a radially inward, compressive force closes theslots at the flanged region, the leafs spring back to substantially thesame positioning that existed before the compressive force was appliedwhen the compressive force is removed.
 6. The replacement thermal sleeveof claim 1, wherein adjacent slots of the plurality of slots each definea leaf portion of the tubular body which extends from the bottom end tothe top end; and wherein, in a relaxed state, at the flanged region, theleafs substantially touch each adjacent leaf and the leafs areconfigured so that if spread apart at the flanged region to a pointwhere the width of the slot is sufficient to seat the flange in a recessin an opening of a head penetration adaptor in which the flanged regionis to be seated to lock the replacement thermal sleeve in the opening,then the leafs experience plastic deformation.
 7. The replacementthermal sleeve of claim 1, further comprising a tool for altering themaximum outside diameter of the flanged region, wherein the tool isconfigured: to be inserted through the bottom end of the tubular body,extend through the tubular body and through the flanged region, grip theflanged region, and activate from outside the top end of the tubularbody to alter the maximum outside diameter of the flanged region.
 8. Thereplacement thermal sleeve of claim 7, wherein the flanged regionincludes recesses or openings in an end surface thereof which areengaged by the tool to alter the maximum outside diameter of the flangedregion.
 9. The replacement thermal sleeve of claim 1, further comprisinga compression tool for compressing the flanged region, wherein thecompression tool is configured as a retention strap installed below theflanged region.
 10. A method of replacing a damaged thermal sleeve in areactor vessel head adapter that connects a control rod drive mechanismto a reactor vessel head, the method comprising the steps of: accessingthe damaged thermal sleeve from an underside of the reactor vessel head;removing the damaged thermal sleeve; obtaining a replacement thermalsleeve having: an elongated tubular body disposed about a centrallongitudinal axis and extending between a bottom end and a top end; aflanged region disposed at or about the top end which extends radiallyoutward from the tubular body; and a plurality of slots defined in thetubular body, each slot extending through and from the top end towardthe bottom end along a predetermined distance, each slot having a widthwhich is sufficient to narrow a maximum outside diameter of the flangedregion from a first diameter to a second diameter in order to clear anyobstruction in an opening of a tubular member in which the thermalsleeve is to be inserted; altering a maximum outside diameter of theflanged region on the replacement thermal sleeve to an extent to clearany obstruction in the opening in the reactor head adapter that will beencountered in inserting the thermal sleeve to a location within theopening originally occupied by the damaged thermal sleeve; inserting thereplacement thermal sleeve through the opening from the underside of thereactor vessel head; and expanding the maximum outside diameter of theflanged region into a recess in the opening of the reactor head adapter.11. The method of claim 10, wherein altering the maximum outsidediameter of the flanged region comprises exerting a compressive force tocompress adjacent sections of the flanged region together; whereinexpanding the maximum outside diameter of the flanged region comprisesremoving the compressive force.
 12. The method of claim 10, whereinaltering the maximum outside diameter of the flanged region andexpanding the maximum outside diameter of the flanged region areperformed by a tool inserted through the tubular body of the thermalsleeve that engages recesses or openings in an end surface of thetubular body.
 13. The method of claim 10 wherein altering the maximumoutside diameter of the flanged region and expanding the maximum outsidediameter of the flanged region are performed by tightening or releasinga retention strap installed below the flanged region.
 14. The method ofclaim 10, wherein altering the maximum outside diameter of the flangedregion is performed during manufacture of the replacement thermal sleeveand expanding the maximum outside diameter of the flanged region isperformed from the underside of the reactor vessel head adapter.
 15. Areplacement thermal sleeve comprising: a plurality of leafs, each leafextending axially between a bottom end and a top end, with each leafhaving an outwardly, radially extending flange lug disposed at or aboutthe tope end, such that when the leafs are fitted together configure atubular body of the replacement thermal sleeve; and a fastener forfastening the plurality of leafs together.
 16. The replacement thermalsleeve of claim 15, wherein the plurality of leafs are configured to beinserted one at a time into an opening in an underside of a reactor headadapter and the fastener is configured to be applied from an undersideof the reactor head adaptor.
 17. The replacement thermal sleeve of claim15, wherein the plurality of leafs comprises three leafs.
 18. A methodof replacing a damaged thermal sleeve in a reactor vessel head adapterthat connects a control rod drive mechanism to a reactor vessel head,the method comprising the steps of: accessing the damaged thermal sleevefrom an underside of the reactor vessel head adapter; removing thedamaged thermal sleeve; obtaining a replacement thermal sleeve dividedinto a plurality of leafs; inserting the plurality of leafs into anopening in the underside of the reactor vessel head adapter, one at atime; arranging the leafs within the opening into a tubular housing ofthe replacement thermal sleeve; and fastening the leafs together fromthe underside of the reactor vessel head adapter.